The expression icmp eq (select (icmp eq x, 0), 1, x), 0 folds to false.

Spotted by my super-optimizer in 186.crafty and 450.soplex.  We really
need a proper infrastructure for handling generalizations of this kind
of thing (which occur a lot), however this case is so simple that I decided
to go ahead and implement it directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143214 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index 6bef0aedeec4b17c65225ec5ed409b8138da8ec7..83881deccf4069253c9e6454d22708db16195ebd 100644 (file)
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -416,39 +416,55 @@ static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
   }
   assert(isa<SelectInst>(LHS) && "Not comparing with a select instruction!");
   SelectInst *SI = cast<SelectInst>(LHS);
+  Value *Cond = SI->getCondition();
+  Value *TV = SI->getTrueValue();
+  Value *FV = SI->getFalseValue();
 
   // Now that we have "cmp select(Cond, TV, FV), RHS", analyse it.
   // Does "cmp TV, RHS" simplify?
-  if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD, DT,
-                                    MaxRecurse)) {
-    // It does!  Does "cmp FV, RHS" simplify?
-    if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD, DT,
-                                      MaxRecurse)) {
-      // It does!  If they simplified to the same value, then use it as the
-      // result of the original comparison.
-      if (TCmp == FCmp)
-        return TCmp;
-      Value *Cond = SI->getCondition();
-      // If the false value simplified to false, then the result of the compare
-      // is equal to "Cond && TCmp".  This also catches the case when the false
-      // value simplified to false and the true value to true, returning "Cond".
-      if (match(FCmp, m_Zero()))
-        if (Value *V = SimplifyAndInst(Cond, TCmp, TD, DT, MaxRecurse))
-          return V;
-      // If the true value simplified to true, then the result of the compare
-      // is equal to "Cond || FCmp".
-      if (match(TCmp, m_One()))
-        if (Value *V = SimplifyOrInst(Cond, FCmp, TD, DT, MaxRecurse))
-          return V;
-      // Finally, if the false value simplified to true and the true value to
-      // false, then the result of the compare is equal to "!Cond".
-      if (match(FCmp, m_One()) && match(TCmp, m_Zero()))
-        if (Value *V =
-            SimplifyXorInst(Cond, Constant::getAllOnesValue(Cond->getType()),
-                            TD, DT, MaxRecurse))
-          return V;
-    }
+  Value *TCmp = SimplifyCmpInst(Pred, TV, RHS, TD, DT, MaxRecurse);
+  if (!TCmp) {
+    // It didn't simplify.  However if "cmp TV, RHS" is equal to the select
+    // condition itself then we can replace it with 'true'.
+    if (match(Cond, m_ICmp(Pred, m_Specific(TV), m_Specific(RHS))))
+      TCmp = getTrue(Cond->getType());
+  }
+  if (!TCmp)
+    return 0;
+
+  // Does "cmp FV, RHS" simplify?
+  Value *FCmp = SimplifyCmpInst(Pred, FV, RHS, TD, DT, MaxRecurse);
+  if (!FCmp) {
+    // It didn't simplify.  However if "cmp FV, RHS" is equal to the select
+    // condition itself then we can replace it with 'false'.
+    if (match(Cond, m_ICmp(Pred, m_Specific(FV), m_Specific(RHS))))
+      FCmp = getFalse(Cond->getType());
   }
+  if (!FCmp)
+    return 0;
+
+  // If both sides simplified to the same value, then use it as the result of
+  // the original comparison.
+  if (TCmp == FCmp)
+    return TCmp;
+  // If the false value simplified to false, then the result of the compare
+  // is equal to "Cond && TCmp".  This also catches the case when the false
+  // value simplified to false and the true value to true, returning "Cond".
+  if (match(FCmp, m_Zero()))
+    if (Value *V = SimplifyAndInst(Cond, TCmp, TD, DT, MaxRecurse))
+      return V;
+  // If the true value simplified to true, then the result of the compare
+  // is equal to "Cond || FCmp".
+  if (match(TCmp, m_One()))
+    if (Value *V = SimplifyOrInst(Cond, FCmp, TD, DT, MaxRecurse))
+      return V;
+  // Finally, if the false value simplified to true and the true value to
+  // false, then the result of the compare is equal to "!Cond".
+  if (match(FCmp, m_One()) && match(TCmp, m_Zero()))
+    if (Value *V =
+        SimplifyXorInst(Cond, Constant::getAllOnesValue(Cond->getType()),
+                        TD, DT, MaxRecurse))
+      return V;
 
   return 0;
 }

diff --git a/test/Transforms/InstSimplify/compare.ll b/test/Transforms/InstSimplify/compare.ll
index 57727c9ab769169f1c97fcd4f1860fcb4cabbe68..df331225743d0426a70352a074f9fad3ec5f2d15 100644 (file)
--- a/test/Transforms/InstSimplify/compare.ll
+++ b/test/Transforms/InstSimplify/compare.ll
@@ -204,6 +204,15 @@ define i1 @select4(i1 %cond) {
 ; CHECK: ret i1 %cond
 }
 
+define i1 @select5(i32 %x) {
+; CHECK: @select5
+  %c = icmp eq i32 %x, 0
+  %s = select i1 %c, i32 1, i32 %x
+  %c2 = icmp eq i32 %s, 0
+  ret i1 %c2
+; CHECK: ret i1 false
+}
+
 define i1 @urem1(i32 %X, i32 %Y) {
 ; CHECK: @urem1
   %A = urem i32 %X, %Y